I saw a link to what appeared to be a Carbon bike on amazon. The price was extremely lower than any carbon bike I had ever seen. After reading a bit, it seems that the bike frame is really made of "carbon fibre wrapped aluminum". What advantages would wrapping an aluminum frame in carbon have compared to just a regular aluminum bike. Is it just to get a carbon look bike more cheaply, or does it allow you to use a narrower aluminum frame, with carbon taking up some stress, creating a frame with a weight somewhere between carbon and aluminum?

4 Answers
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That is purely marketing. It's a common ploy with components, but I've never seen it on an entire frame until now. Aluminum and carbon can be used in conjunction effectively, but not in this case. The carbon wrap on that bike is basically veneer. While Schwinn was once upon a time a well respected brand, they suffered a major fall from grace after going bankrupt. Their bikes, even their bike shop level bikes (i think they call them their "select" series bikes) target the budget market. They're not horrible, but they're not great either. The bike you posted a link to is no exception. One could argue that the combination of dissimilar materials would aid to vibration dampening, but that's really just more marketing jargon, at least in this case. That bike will still ride just like a full aluminum framed bike would. If you are considering that bike save yourself a few bucks and just go with a full aluminum frame.

One COULD do the carbon wrapped aluminum trick and have a useful result -- build the frame out of very thin aluminum and then wrap fairly heavily with carbon. In some ways this manufacturing technique might be cheaper than conventional carbon, and it should produce a bike with most of the better attributes of carbon, plus the tricky aspects of joining carbon to bearing races would be simplified. But of course it's unlikely that the subject bike is much of a step in this direction.
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Daniel R HicksNov 21 '11 at 22:03

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My assumption is that if there was benefit to be had and it could be done, some reputable manufacturer would have already jumped on the process.
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joelmdevNov 21 '11 at 23:03

There simply aren't that many customers for such a scheme. The real bike junkies insist on having the most expensive carp available, while the bulk of the cycling public simply wants a bike that will get them from A to B (and maybe look sexy along the way).
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Daniel R HicksNov 22 '11 at 0:33

For the carbon fiber to be of any use structurally, it has have multiple layers. If it says it is wrapped around the aluminum, my bet it is for show only so it gives the appearance of being an expensive frame when it is clearly not.

There is no way that a composite of the two will be very light without being very weak if it were compared to a full Carbon frame or an Aluminum. Both materials will not hold up to a stress test. The Aluminum would be very brittle and the Carbon fiber would be very squishy.

Carbon and Aluminum are very light as is. Carbon fiber is light and when wrapped certain ways can be stiff or supple. Aluminum is always stiff, that is the nature of the material.

To reiterate, it is most likely a way to mask a cheap frame and pass it off as Carbon fiber.

You're certainly right that the carbon wrap is just to make this cheap bicycle look fancier than it is. You're not right that aluminum is always stiff and brittle; old ALAN aluminum frames are quite flexy. For metal frames, tubing thickness and diameter play a significant role in how the frame behaves.
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lantiusNov 21 '11 at 19:10

-1: It is not in aluminum's nature to be stiff. Aluminum is typically stiff in bicycle frames, because of engineering trade offs that have to be made in strength vs stiffness which are realized by the geometry of the tubing.
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whatsisnameNov 22 '11 at 16:41

@freiheit: brittle has a special meaning in engineering, where brittle materials break without much deformation. Aluminum will deform quite a bit before it ultimately breaks in non-fatigue failures. Concrete and carbon fibers don't deform, those are brittle materials. As for the fatigue limit on aluminum, "eventually" can take potentially millions or billions+ of cycles before it eventually fractures, depending on the magnitude of the involved stresses.
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whatsisnameNov 22 '11 at 19:57

It would in theory combine some of the characteristics of both, while permitting a cheaper bike than straight carbon. The aluminum could be thinner, providing only modest strength but serving as a mandrel to support the carbon, and the carbon would produce a stiffer bike than straight aluminum.

Or it could just be hype. Or the "carbon wrap" could be used to conceal crummy joining of the aluminum tubes.

Mid range bikes commonly have a carbon-wrapped seat post which claims to reduce vibration and increase comfort. Basically, get some of the benefits of a full carbon seat post with less of the cost. I expect this manufacturer is using the same concept on the entire frame to get carbon-like ride at a reduced cost.

Personally, I cannot discern the difference between a carbon-wrapped and a non-carbon wrapped seat post. I know other riders who believe it makes a difference (but they were using a different brand of seatpost).

I think it's difficult to tell if the carbon-wrap would improve the ride any just based on the description. I've ridden aluminum frame bikes that ride far better than full-carbon frame bikes that cost quite a bit more. The frame material is just one factor in ride quality and a "carbon wrapped" frame could be a huge improvement for the right frame design or a huge marketing gimmick for the wrong one.